Joining of amorphous metals to other metals utilzing a cast mechanical joint

ABSTRACT

The present invention is directed to a method of joining an amorphous material to a non-amorphous material including, forming a cast mechanical joint between the bulk solidifying amorphous alloy and the non-amorphous material.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority on U.S. provisional application No.60/309,767 filed on Aug. 2, 2001, the content of which is incorporatedherein by reference.

FIELD OF THE INVENTION

The present invention is related to methods for joining bulk solidifyingamorphous alloys with non-amorphous metals.

BACKGROUND OF THE INVENTION

Bulk solidifying amorphous alloys are a family of amorphous alloys whichcan be cooled from the molten state at substantially lower coolingrates, about 500 K/sec or less, than older conventional amorphous alloysand still substantially retain their amorphous atomic structure. Assuch, they may be produced in amorphous form and with thicknesses of 1millimeter or more, significantly thicker than possible with the olderamorphous alloys that require much higher cooling rates.Bulk-solidifying amorphous alloys have been described, for example, inU.S. Pat. Nos. 5,288,344; 5,368,659; 5,618,359; and 5,735,975, thedisclosures of which are incorporated by reference.

A family of bulk-solidifying alloys of most interest may be described bythe molecular equation: (Zr,Ti)_(a)(Ni,Cu,Fe)_(b)(Be,Al,Si,B)_(c), wherea is in the range of from about 30 to about 75, b is in the range offrom about 5 to about 60, and c is in the range of from 0 to about 50,in atomic percentages. These alloys can accommodate substantial amountsof other transition metals, up to about 20 atomic percent, andpreferably metals such as Nb, Cr, V, and Co. A preferred alloy family is(Zr,Ti)_(d)(Ni,Cu)_(e)(Be)_(f), where d is in the range of from about 40to about 75, e is in the range of from about 5 to about 60, and f is inthe range of from about 5 to about 50, in atomic percentages. Still amore preferably composition is Zr₄₁Ti₁₄Ni₁₀Cu_(12.5) Be_(22.5), inatomic percentages. Bulk solidifying amorphous alloys are desireablebecause they can sustain strains up to about 1.5 percent or more withoutany permanent deformation or breakage; they have high fracture toughnessof about 10 ksi sqrt(in) or more (sqrt denotes square root), andpreferably 20 ksi sqrt(in) or more; and they have high hardness valuesof 4 GPa or more, and preferably 5.5 GPa or more. In addition todesirable mechanical properties, bulk solidifying amorphous alloys alsohave very good corrosion resistance.

Because the properties of the bulk solidifying amorphous alloys may notbe needed for some parts of the structure, and because they arerelatively expensive compared to non-amorphous materials, such asaluminum alloys, magnesium alloys, steels, and titanium alloys manycases, bulk solidifying amorphous alloys are typically not used toproduce an entire structure. It is therefore necessary to join is thebulk solidifying amorphous alloy portion of the structure to the portionof the structure that is the non-amorphous solidifying alloy.

A number of different joining methods have been explored including:mechanical fasteners, which may be used in some cases, but they havedisadvantages in both mechanical properties and physical properties,such as corrosion resistance, when in contact with the bulk solidifyingamorphous alloy; adhesives, which may be used, but only if the servicetemperature is sufficiently low that the adhesive retains its strength;and finally, brazing and welding, which are possibilities, butsatisfactory techniques and materials have not been developed for thebrazing and welding of amorphous materials.

Accordingly, a need exists for a method of joining amorphous materialsto non-amorphous materials in an inexpensive, but robust manner.

SUMMARY OF THE INVENTION

The present invention is directed to a method of joining abulk-solidifying amorphous material to a non-amorphous materialincluding, forming a cast mechanical joint between the bulk solidifyingamorphous alloy and the non-amorphous material.

In a first embodiment, the joint is formed by controlling the meltingpoint of the non-amorphous and bulk-solidifying amorphous alloys(amorphous metals). In one such embodiment, where the non-amorphousmetal has a higher melting point than the melting point of the amorphousmetal, the non-amorphous metal is properly shaped and thebulk-solidifying amorphous alloy is melted and cast against the piece ofpreformed non-amorphous metal by a technique such as injection or diecasting. In another such embodiment, where the non-amorphous metal has alower melting point than the melting point of the amorphous metal, thenon-amorphous material may be joined to the bulk-solidifying amorphousalloy by melting the non-amorphous alloy and casting it, as by injectionor die casting, against a piece of the properly shaped and configuredbulk-solidifying amorphous alloy which remains solid.

In a second embodiment, the joint is formed by controlling the coolingrate of the non-amorphous and amorphous metals. In one such embodiment,a non-amorphous metal is cast against a piece of pre-formedbulk-solidifying amorphous alloy, and cooled from the castingtemperature of the non-amorphous alloy down to below the glasstransition temperature of bulk-solidifying amorphous alloy at rates atleast about the critical cooling rate of bulk solidifying amorphousalloy.

In either of the above embodiments, a system, such as a heat sink may beprovided to ensure that the temperature of either the pre-formedamorphous metal or pre-formed non-amorphous metal always stay below theglass transition temperature of the bulk-solidifying amorphous alloy.

In still another embodiment, the shapes of the pieces of thebulk-solidifying amorphous alloy and the non-amorphous metal areselected to produce mechanical interlocking of the final pieces.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the invention will beapparent from the following detailed description, appended claims, andaccompanying drawings, in which:

FIG. 1 is a flow chart of a method according to a first exemplaryembodiment of the current invention;

FIG. 2 is a flow chart of a method according to a second exemplaryembodiment of the current invention;

FIG. 3 is a schematic Time-Temperature-Transformation (“TTT”) diagram ofan amorphous metal according to the invention.;

FIG. 4 is a flow chart of a method according to a third exemplaryembodiment of the current invention;

FIG. 5 is a schematic of an exemplary joint according to the presentinvention; and

FIG. 6 is a schematic of an exemplary joint according to the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to a method of joining abulk-solidifying amorphous alloy to a non-amorphous metal.

The bulk solidifying amorphous alloys are a family of amorphous alloyswhich can be cooled from the molten state at substantially lower coolingrates, about 500 K/sec or less, than older conventional amorphous alloysand still substantially retain their amorphous atomic structure. Assuch, they may be produced in amorphous form and with thicknesses of 1millimeter or more, significantly thicker than possible with the olderamorphous alloys that require much higher cooling rates. Bulksolidifying amorphous alloys have been described, for example, in U.S.Pat. Nos. 5,288,344; 5,368,659; 5,618,359; and 5,735,975, thedisclosures of which are incorporated by reference.

A family of bulk-solidifying alloys of most interest may be described bythe molecular equation: (Zr,Ti)_(a)(Ni,Cu,Fe)_(b)(Be,Al,Si,B)_(c), wherea is in the range of from about 30 to about 75, b is in the range offrom about 5 to about 60, and c is in the range of from 0 to about 50,in atomic percentages. These alloys can accommodate substantial amountsof other transition metals, up to about 20 atomic percent, andpreferably metals such as Nb, Cr, V, and Co. A preferred alloy family is(Zr, Ti)_(d)(Ni,Cu)_(e)(Be)_(f), where d is in the range of from about40 to about 75, e is in the range of from about 5 to about 60, and f isin the range of from about 5 to about 50, in atomic percentages. Still amore preferably composition is Zr₄₁Ti₁₄Ni₁₀Cu_(12.5)Be_(22.5), in atomicpercentages. Another preferable alloy family is (Zr)_(a)(Nb,Ti)_(b)(Ni,Cu)_(c)(Al)_(d), where a is in the range of from 45 to65, b is in the range of from 0 to 10, c is in the range of from 20 to40 and d in the range of from 7.5 to 15 in atomic percentages. Bulksolidifying amorphous alloys can sustain strains up to about 1.5 percentor more without any permanent deformation or breakage. They have highfracture toughness of about 10 ksi-sqrt(in) or more (sqrt denotes squareroot), and preferably 20 ksi sqrt(in) or more. Also, they have highhardness values of 4 GPa or more, and preferably 5.5 GPa or more. Inaddition to desirable mechanical properties, bulk solidifying amorphousalloys also have very good corrosion resistance.

Another set of bulk-solidifying amorphous alloys are compositions basedon ferrous metals (Fe, Ni, Co). Examples of such compositions aredisclosed in U.S. Pat. No. 6,325,868; (A. Inoue et. al., Appl. Phys.Lett., Volume 71, p 464 (1997)); (Shen et. al., Mater. Trans., JIM,Volume 42, p 2136 (2001)); and Japanese patent application 2000126277(Publ. #.2001303218 A), all of which are incorporated herein byreference. One exemplary composition of such alloys isFe₇₂Al₅Ga₂P₁₁C₆B₄. Another exemplary composition of such alloys isFe₇₂Al₇Zr₁₀Mo₅W₂B₁₅. Although, these alloy compositions are notprocessable to the degree of the Zr-base alloy systems, they can bestill be processed in thicknesses around 1.0 mm or more, sufficientenough to be utilized in the current invention.

In general, crystalline precipitates in bulk-solidifying amorphousalloys are highly detrimental to the alloys' properties, especially tothe toughness and strength of such alloys, and, as such, it is generallypreferred to minimize the volume fraction of these precipitates as muchas possible. However, there are cases in which ductile crystallinephases precipitate in-situ during the processing of bulk-solidifyingamorphous alloys that are indeed beneficial to the properties ofbulk-solidifying amorphous alloys, and especially to the toughness andductility. Such bulk-solidifying amorphous alloys comprising suchbeneficial precipitates are also included in the current invention. Oneexemplary case is disclosed in (C. C. Hays et. al, Physical ReviewLetters, Vol. 84, p 2901, 2000), the disclosure of which is incorporatedherein by reference.

The second metal, which is generally termed herein the “non-amorphous”metal because it is normally non-amorphous in both that it has adifferent composition and that it is a conventional crystalline metal inthe case of a metal, may be chosen from any suitable non-amorphousmetals including, for example, aluminum alloys, magnesium alloys,steels, nickel-base alloys, copper alloys and titanium-base alloys, etc.

The invention is first directed to a method of joining thebulk-amorphous alloy to the non-amorphous metal. As shown in FIGS. 1 and2, there are two different methods depending on the relative physicalproperties of the metals.

In the first exemplary embodiment, as shown in FIG. 1, a method isprovided for joining a non-amorphous metal, which has a higher meltingpoint, to a bulk-solidifying amorphous alloy that has a lower relativemelting point. Although amorphous materials do not experience a meltingphenomenon in the same manner as a crystalline material, it isconvenient to describe a “melting point” at which the viscosity of thematerial is so low that, to the observer, it behaves as a melted solid.The melting point or melting temperature of the amorphous metal may beconsidered as the temperature at which the viscosity of the materialfalls below about 102 poise. Alternatively, it can be convenient to takethe melting temperature of the crystalline phases of thebulk-solidifying amorphous alloy composition as the melting temperatureof the amorphous metal.

For example, the melting points of steels, nickel-base alloys, and mosttitanium-base alloys are greater than the melting point of most bulksolidifying amorphous alloys. In this case, the non-amorphous metal isproperly shaped and configured and remains a solid (step 1), and thebulk-solidifying amorphous metal is melted (step 2) and cast (step 3)against the piece of the pre-formed non-amorphous metal by a techniquesuch as injection or die casting. Where the bulk-solidifying amorphousalloy is the metal that is melted, it must also be cooled (step 4)sufficiently rapidly to achieve the amorphous state at the completion ofthe processing, but such cooling is within the range achievable in suchcasting techniques. The rapid cooling may be achieved by any operableapproach. In one example, the rapid cooling of the meltedbulk-solidifying amorphous alloy when it contacts the non-amorphousmetal and the mold is sufficient. In other cases, the entire mold withthe enclosed metals may be rapidly cooled following casting.

In a further preferred alternative embodiment, as shown in the dashedbox (optional step 3 a), a further heat sink, or like temperaturemaintenance system, is provided to the non-amorphous metal preformedpart to ensure that the part does not exceed the glass transitiontemperature (T_(g)) of the bulk-solidifying amorphous alloy piece suchthat the stored heat in the non-amorphous part does not cause theamorphous alloy to flow or crystallize during or after the castingprocess. The heat sink can be a passive one, such as the case where thepreformed non-amorphous metal part is massive enough to be the heat sinkitself. Alternatively, the heat sink can be an active (or external) one,such as mold or die walls with intimate or close contact with thepre-formed non-amorphous metal part. Finally, the heat sink can beachieved by actively cooling a piece of the bulk-solidifying amorphousalloy casting (which is in intimate or close contact with the pre-formednon-amorphous metal part). This active cooling can also be achievedthrough mold or die walls.

In the second exemplary method, depicted in a flow-chart in FIG. 2, thenon-amorphous metal has a lower melting point than the melting point ofthe amorphous metal.

In one example, a bulk-solidifying amorphous alloy as described above,is joined to a low-melting point non-amorphous metal, such as analuminum alloy. The melting point of a typical amorphous metal, asdescribed above, is on the order of 800° C. The melting point of mostaluminum alloys is about 650° C. or less. In such an exemplaryembodiment, a piece of the aluminum alloy (or other lower-melting-pointalloy, such as a magnesium alloy) may be joined to a piece of thebulk-solidifying amorphous alloy (step 1) by melting the aluminum alloy(step 2) and casting it, as by injection or die casting, against a pieceof the properly shaped and configured bulk-solidifying amorphous alloywhich remains solid (step 3) as shown in FIG. 2.

In this embodiment of the invention, to ensure that the bulk-solidifyingamorphous alloy remains solid, a heat sink is provided which keeps thebulk-solidifying amorphous alloy at a temperature below the transitionglass temperature (T_(g)) of the bulk-solidifying amorphous alloy. Theheat sink can be a passive one, such as in the case where the preformedbulk-solidifying amorphous alloy part is massive enough to be the heatsink itself. Alternatively, the heat sink can also be an active (orexternal) one, such as the mold or die walls in intimate or closecontact with the piece of preformed bulk-solidifying amorphous alloy.Finally, the heat sink can also be achieved by actively cooling thecasting of the non-amorphous metal (which is in intimate or closecontact with the piece of pre-formed bulk-solidifying amorphous alloy).This cooling can also be achieved through mold or die walls.

Although the above embodiments depend on the physical properties, i.e.,melting temperatures of the amorphous and non-amorphous metals, itshould be understood that by controlling the cooling rate of the moltenor cast metals that such limitations are not required. Specifically, bycontrolling the cooling rate of the cast metals to preventcrystallization of the amorphous metal either of the metals, regardlessof their relative melting temperatures, could be utilized as the “castmetal”.

The crystallization behavior of bulk-solidifying amorphous alloys whenit is undercooled from a molten liquid to below its equilibrium meltingpoint T_(melt) can be graphical illustrated usingTime-Temperature-Transformation (“TTT”) diagrams, an illustrativeTTT-diagram is shown in FIG. 3. It is well known that if the temperatureof an amorphous metal is dropped below the melting temperature the alloywill ultimately crystallize if not quenched to the glass transitiontemperature before the elapsed time exceeds a critical value, t_(x)(T).This critical value is given by the TTT-diagram and depends on theundercooled temperature. Accordingly, the bulk-solidifying amorphousalloy must be initially cooled sufficiently rapidly from above themelting point to below the glass transition temperature (T_(g))sufficiently fast to bypass the “nose region” of the material'sTTT-diagram (T_(nose), which represents the temperature for which theminimum time to crystallization of the alloy will occur) and avoidcrystallization (as shown by the arrow in FIG. 3).

In one exemplary embodiment of such a process, summarized in the flowchart shown in FIG. 4, a non-amorphous metal is cast against a piece ofpre-formed bulk-solidifying amorphous alloy. In this embodiment, thenon-amorphous metal is cooled from the casting temperature of thenon-amorphous metal down to below the glass transition temperature ofthe bulk-solidifying amorphous alloy at rates higher than the criticalcooling rate of the bulk solidifying amorphous alloy. By controlling thecooling rate of the non-amorphous metal being cast, the preformed bulkamorphous metal piece remains in the left portion of its TTT diagram, inthe non-crystallization region (FIG. 3). In such an embodiment,preferably, the non-amorphous metal is cooled from the castingtemperature of non-amorphous metal down to below the glass transitiontemperature of the bulk-solidifying amorphous alloy at rates higher thantwice the critical cooling rate of bulk solidifying amorphous alloy toensure that no portion of the amorphous metal piece is crystallized.

Several casting methods can be implemented to provide the sufficientcooling rate. For example, metallic mold casting, die-casting(especially for aluminum, zinc, magnesium alloys), etc. Although thismethod can be performed independent of the melting temperatures of thetwo metals, it is preferable if the bulk solidifying amorphous alloy hasa higher melting temperature than the non-amorphous metal. Controllingfor both cooling rate and melting temperature ensures that thetemperature of the bulk amorphous alloy always remains below its meltingtemperature during casting so that the viscosity and activity of thebulk amorphous alloy is kept at reduced levels, which in turn preventsunwanted intermetallics from forming at the interface of the twomaterials from metallurgical reactions.

This invention is also directed to articles formed by the joiningmethods discussed above. In one exemplary embodiment, the shapes of thepieces of the bulk-solidifying amorphous alloy and the non-amorphousmetal are selected to produce mechanical interlocking of the finalpieces. FIGS. 5 and 6 illustrate such an approach. In FIGS. 5 and 6,metal A is the non-amorphous metal, and metal B is the bulk-solidifyingamorphous alloy.

Referring to FIG. 5, it can be seen that if metal A has a lower meltingpoint than metal B (first case above), metal B is machined to have aninterlocking shape 10. Metal A is then melted and cast against metal B,filling and conforming to the interlocking shape 10. Upon cooling metalA solidifies into interlocking shape 12 and the two pieces 10 and 12 aremechanically locked together.

Alternatively, as shown in FIG. 6 if the non-amorphous metal A has ahigher melting point than the bulk-solidifying amorphous alloy metal B(second case above), the metal A is machined to have the interlockingshape 10. Metal B is then melted and cast against metal A, filling andconforming to the interlocking shape 10. Upon cooling metal B solidifiesto form interlocking shape 12 and the two pieces metal A and metal B aremechanically locked together.

Although only two different interlocking shapes are shown in FIGS. 5 and6, it should be understood that any suitable interlocking shape may beutilized in the current invention such that there is a mechanicalinterference that prevents the separation of metal A and metal B, afterthe casting process is complete.

Although the method of the current invention is designed such that themetals are permanently mechanically locked together, such pieces beseparated by melting the metal having the lower melting point to saidmelting point.

In addition, although the joining of only two separate pieces isdiscussed in the current invention, it should be understood that themethod of the current invention may be utilized to join an arbitrarynumber of bulk-solidifying alloy and non-amorphous metal articlestogether.

Although specific embodiments are disclosed herein, it is expected thatpersons skilled in the art can and will design alternative methods tojoin bulk-solidifying amorphous alloys to non-amorphous metals that arewithin the scope of the following description either literally or underthe Doctrine of Equivalents.

What is claimed is:
 1. A method of joining a bulk-solidifying amorphousalloy material to a non-amorphous metal material wherein the meltingtemperature of the bulk-solidifying amorphous alloy material is higherthan the melting temperature of the non-amorphous material, comprising:providing a pre-formed piece, wherein the pre-formed piece is made ofthe bulk-solidifying amorphous alloy material; casting a second piece ata casting temperature in a joining relationship with said pre-formedpiece to form a single integral article, wherein the second piece ismade of the non-amorphous metal material, and wherein the castingtemperature is greater than the melting temperature of the non-amorphousmetal material; and cooling the single integral article at a ratesufficient to ensure that the bulk-solidifying amorphous alloy materialremains substantially amorphous.
 2. The method as described in claim 1,wherein a heat sink is further provided to maintain the temperature ofthe preformed piece below the glass transition temperature of thebulk-solidifying amorphous alloy.
 3. A method of joining abulk-solidifying amorphous alloy material to a non-amorphous metalmaterial, comprising: providing a pre-farmed piece, wherein thepre-formed piece is made of a bulk-solidifying amorphous alloy material;casting a second piece from a non-amorphous material at a castingtemperature above the melting temperature of the non-amorphous materialin a joining relationship with said pro-formed piece; and cooling thesecond piece at a rate at least about the critical cooling rate of thebulk-solidifying amorphous alloy material to form a single integralarticle.
 4. The method as described in claim 3 wherein thebulk-solidifying amorphous alloy material is described by the equation:(Zr,Ti)_(a)(Ni,Cu,Fe)_(b)(Be,Al,Si,B)_(c) where a is in the range offrom about 30 to about 75, b is in the range of from about 5 to about60, and c is in the range of from 0 to about 50, in atomic percentages.5. The method as described in claim 4, wherein the bulk-solidifyingamorphous alloy material includes up to about 20 atomic percent of atleast one additional transition metal.
 6. The method as described inclaim 3, wherein the bulk-solidifying amorphous alloy material isdescribed by the equation: (Zr, Ti)_(d)(Ni, Cu)_(e)(Be)_(f) where d isin the range of from about 40 to about 75, e is in the range of fromabout 5 to about 60, and f is in the range of from about 5 to about 50,in atomic percentages.
 7. The method as described in claim 3, whereinthe bulk-solidifying amorphous alloy material is described by theequation: (Zr)_(a) (Nb,Ti)_(b) (Ni,Cu)_(c)(Al)_(d), where a is in therange of from 45 to 65, b is in the range of from 0 to 10, c is in therange of from 20 to 40 and d in the range of from 7.5 to 15 in atomicpercentages.
 8. The method as described in claim 3, wherein thenon-amorphous material is selected from the group consisting at aluminumalloys, magnesium alloys, and copper alloys.
 9. The method as describedin claim 3, wherein the non-amorphous material is selected from thegroup consisting of: steels, nickel alloys, titanium alloys, and copperalloys.
 10. The method as described in claim 3, wherein the pre-formedand second pieces are designed to mechanical interlock in the singleintegral article.
 11. The method as described in claim 3, wherein thepreformed piece is cooled at a rate at least about twice the criticalcooling rate of the bulk-solidifying amorphous alloy material.
 12. Themethod as described in claim 3, wherein the step of cooling includesactively quenching both the preformed and second pieces.
 13. The methodas described in claim 3, wherein the rate of cooling is about 500 K/secor less.
 14. The method as described in claim 3, wherein the step ofcasting is selected from the group consisting of: injection casting, diecasting, and mold casting.
 15. The method as described in claim 3,wherein the melting temperature of the material being cast is less thanthe melting temperature of the material in the preformed piece.
 16. Anarticle made in accordance with the method described in claim
 3. 17. Thearticle as described in claim 16, wherein the preformed and secondpieces mechanically interlock to form a single integral piece.